1. Field of the Invention
This invention relates generally to a circuit closing device that is disabled by an undervoltage condition, and more specifically, this invention relates to a circuit closing device that opens a power line protected by a ground fault current interrupter circuit in the event that the neutral conductor is broken.
2. Description of the Prior Art
Ground fault current interrupter circuits are in general usage to protect people and equipment from undesired ground fault currents. These ground fault current interrupter circuits have conventionally been mounted in fixed locations, such as, for example, in association with an electrical outlet. Accordingly, the size of the ground fault current interrupter circuit, within limits, has not been a significant problem.
As the technology in this area has advanced, other uses for ground fault current interrupter circuits have been considered. As a result, many applications for ground fault current interrupter circuits in which a fixed mounting is not possible have been eyed. Accordingly, various efforts have been made to develop a ground fault current interrupter circuit that could be incorporated into a plug or portable receptacle. As currently existing, the results of these efforts have produced devices that have been undesirably bulky and unduly costly.
One of the difficulties that is encountered in portable situations is that the possibility of a broken neutral conductor is greatly increased. This means that you could still have a potentially dangerous fault from the "hot" or "live" power line to ground, but there would be no power across the ground fault current interrupter circuit to provide the desired protection. Therefore, Underwriters Laboratories has a requirement that all non-permanently connected ground fault current interrupter circuits must be protected against the possibility of a broken neutral conductor.
Currently available systems including such protection against a broken neutral conductor employ a relay energized from the power line to close the circuit from the power to the load. While such an approach is effective to protect against a broken neutral conductor, since a broken neutral would result in de-energization of the relay and hence breaking of the power line to a load, the relays required are relatively large and bulky, relatively expensive and consume undesirably large amounts of power. The result is that the use of non-permanently connected ground fault current interrupter circuits in this country has been greatly hindered.
Other countries which do not have the UL requirement for protection against a broken neutral exhibit the very large potential uses for such non-permanently connected circuits, as some of these countries use many times the number of non-permanently connected ground fault current interrupter circuits that are employed in the United States. Of course, the hazard exists in these countries of a dangerous fault condition being created by a broken neutral, and a certain number of injuries are encountered. Accordingly, these countries also need an effective and relatively inexpensive protection against a broken neutral conductor.